1. Technical Field
The present invention relates to an optical pointing apparatus, and relates more particularly to an optical pointing apparatus comprising an image-capturing device.
2. Related Art
Pointing apparatuses such as an electronic mouse are devices that can detect their displacements relative to their supporting surfaces. A user grasps a pointing apparatus and slides the pointing apparatus on a planar surface. The pointing apparatus may compute its displacement relative to the planar surface, and may use the displacement as an input signal sent to a computer. A conventional pointing apparatus may compute its displacement according to the number of rolling cycles counted by the roller on the apparatus as the device rolls on a surface. However, accumulated dust may adversely affect the accuracy of the calculation of the displacement of the roller pointing apparatus after the roller pointing apparatus has been used for a long time. Due to such disadvantage, with the development of technology, optical pointing apparatuses such as the optical mouse increasingly replace such roller pointing apparatuses.
Optical pointing apparatuses similarly detect their displacements relative to their supporting surfaces. Unlike conventional roller pointing apparatuses, optical pointing apparatuses detect their displacements based on reflective light. FIG. 1 shows a conventional optical pointing apparatus. As shown in FIG. 1, the optical pointing apparatus 100 comprises a light source 102, a focus lens 104, a light extraction lens 106, a sensing device 108, and a processing unit 110. The light source 102 may be an LED (light-emitting diode) based light source or a laser, which projects light through the focus lens 104 onto a planar surface 150. The planar surface 150 reflects the light, and the light extraction lens 106 collects reflective light and brings it to the sensing device 108. The processing unit 110 uses output signals from the sensing device 108 to calculate the displacement of the optical pointing apparatus 100 relative to the planar surface 150.
FIG. 2 shows an enlarged sensing device 108. As illustrated in FIG. 2, the sensing device 108 comprises a plurality of image-sensing elements 200 arranged in an array. The image-sensing elements 200 may capture the image of the planar surface 150 whereby the output signals are generated. The processing unit 110 compares the correlation between two successive images, and determines the displacement of the optical pointing apparatus 100 relative to the planar surface 150 by the relative orientation and distance between two highly correlated regions. For example, if the comparison result from the processing unit 110 shows that the second image is highly correlated with the upper left region of the first image, it can be determined that the optical pointing apparatus 100 is moving in the lower right direction.
Generally, under the condition that the number of image-sensing elements 200 is the same, if the areas of the image-sensing elements 200 are larger, the resolution of the image-sensing elements 200 is lower; while if the areas of the image-sensing elements 200 are smaller, the detectable displacement range is smaller. In other words, regardless whether the areas of the image-sensing elements 200 are large or small, the performance of the optical pointing apparatus 100 has its own limitation. The optical pointing apparatus with large area image-sensing units has poor resolution that causes users to experience non-smooth cursor movements. In contrast, with optical pointing apparatus with small area image-sensing units, the user needs to move the optical pointing apparatus farther to obtain sufficient accuracy of desired input signals, and the optical pointing apparatus with small area image-sensing units leads to a smaller detectable displacement range.
Therefore, the relevant industry needs a new optical pointing apparatus.